The present invention relates in general to aircraft navigation systems and in particular to systems for generating an accurate reference location with a respect to a runway. Still more particularly, the present invention relates to systems for generating position correction signals from optical observation for utilization in the inspection of instrument landing systems.
Instrument landing systems are well known in the prior art. Such systems can be utilized to permit appropriately equipped aircraft to land on airport runways under highly hazardous conditions. However, in order to utilize such systems it is necessary to periodically inspect and calibrate these systems to ensure that the electronic indications of aircraft location are sufficiently accurate with respect to actual aircraft location.
Highly accurate inertial navigation systems are known which generate relatively accurate indications of aircraft location from a selected point; however, these systems are not sufficiently accurate to permit the evaluation of Instrument Landing Systems (ILS). Thus, a more accurate method of generating aircraft location must be utilized.
In order to generate highly accurate reference locations of inspection aircraft, prior art systems have utilized a variety of approaches. For example, one system utilizes a ground-based optical tracking device such as a theodolite to generate a reference location which may be compared to the electronically generated location provided by the instrument landing system. Other systems utilize ground-based optical reflectors which can be utilized to allow an aircraft equipped with light sources and detectors to obtain a reference location.
All such known systems require extensive groundbased equipment and/or operators to generate a reference location of the inspection aircraft. As such, some of these systems are subject to human error and some can only be operated during daylight hours in acceptable weather conditions. Thus, it should be apparent that a need exists for a flight inspection system which does not require extensive ground-based equipment or personnel and which generates a highly accurate reference location with respect to an airport runway.